The present invention relates to an actuator in which thrust of a rod for moving up and down can be controlled.
Upward and downward movements of a rod are normally guided by a guide of a contact type such as a linear guide. When such a rod of contact support is moved up and down by means which can finely control thrust by controlling energization as is the case with a thrust producer of a moving-magnet type, driving control of 5% or less of full thrust is difficult.
The present invention has been accomplished to solve the above problem and it is a technical object of the invention to provide an actuator in which thrust control can be easily carried out even with driving control of 5% or less of full thrust.
To achieve the above object, according to the invention, there is provided an actuator comprising a rod supported for upward and downward movements by an apparatus main body and a thrust producer for producing thrust for moving the rod up and down, wherein the rod is supported in a noncontact state by a bearing portion of the apparatus main body through an air hydrostatic bearing, the thrust producer is of a moving-magnet type including a magnet mounted to the rod to be displaced with the rod and a coil provided to the apparatus main body to generate magnetic force when the coil is energized, and the thrust producer produces the thrust by an interaction of the magnet and the magnetic force generated by the coil.
In the actuator having the above structure, the thrust of the rod can be finely controlled by the thrust producer of the moving-magnet type. Furthermore, because the rod is supported in the noncontact state by the bearing portion of the apparatus main body through the air hydrostatic bearing, driving of 5% or less of full thrust can be easily controlled in driving up and down the rod.
According to a concrete embodiment of the invention, the thrust producer includes two magnets and two coils which can generate different amounts of thrust and energization of which can be controlled individually, one of the coils controls a large load which is mainly weight of the rod, and the other of the coils controls a small load which is mainly upward and downward movements of the rod.
According to another concrete embodiment of the invention, the rod is supported in upper and lower two positions by two air hydrostatic bearings, the thrust producer is disposed between the air hydrostatic bearings, the magnet in the thrust producer is fitted with an outer periphery of the rod, and the coil is disposed to surround an outer periphery of the magnet.
In the invention, it is preferable that the apparatus main body includes a cylindrical casing portion having therein a rod hole, the rod is provided to pass through the rod hole in the casing portion, the bearing portion is provided to each of upper and lower ends of the casing portion, and the thrust producer is provided to the casing portion between the bearing portions.
According to another concrete embodiment of the invention, the rod is rotatable, the apparatus main body includes a motor for rotating the rod, a rotating shaft of the motor and the rod are connected to each other through a joint for transmitting rotation between the rotating shaft and the rod and for allowing axial movements of the rotating shaft and the rod with respect to each other.
In the invention, it is possible that a load cell pressurized by displacement of the rod is provided between the apparatus main body and the rod and that output of the load cell is fed back to a driving system of the thrust producer. In this case, the load cell is mounted onto a support provided to the apparatus main body such that a pressurizing portion is close to the rod, a contact is mounted to the pressurizing portion, and a flange-shaped contact member for coming in contact with the contact is fixed to the rod.